1. Field of the Invention
The invention relates to a catadioptric objective, specifically it relates to a projection exposure objective for semiconductor microlithography, comprising a plurality of lenses and comprising at least two deflecting mirrors that have reflecting surfaces that are at a specific angle, in particular of 90°, to one another.
2. Description of the Related Art
In the case of catadioptric objectives for microlithography, for example in the case of wavelengths of 157 nm, two deflecting mirrors are used that must be at a very precisely defined angle of 90° to one another. This angular position must also be retained exactly. Moreover, the natural frequency of the mirrors must be very high so that no aberrations occur. For this reason, they may also not vibrate relative to one another.
WO 95/30918 discloses binoculars, mirrors being held against reference surfaces and being adjusted in a specific angular position relative to one another. (FIGS. 16 to 20).